The present invention relates to testing the flying height of a head assembly including a read/write head mounted on a slider used in a computer disc drive. In particular, the present invention is a calibration standard and a method of calibrating a flying height tester.
In the disc recording art, it is common to use a read/write head mounted on a slider which reacts against the air moved with the rotating disc, causing the slider and head to "fly" a small distance from the disc surface. In the manufacture of such head assemblies, it is common to test the hydrodynamic characteristics of the assembly so that the flying height characteristics are known, thereby avoiding the use of heads which fly too high or too low in relationship to disc surface and also avoiding heads which fly at an improper angle to the disc. Too high a flying height will result in lower areal density, while too low a flying height can cause head/disc interface failure.
Flying height testing is generally accomplished by means of a flying height tester, using optical interference techniques. Such a flying height tester comprises, for example, a light source directing light at a glass disc. The glass disc is rotated at speeds simulating the rotation of a magnetic disc, and the head assembly being tested is positioned in a holder in flying relation to the glass disc. Light is directed at the disc at a predetermined angle to the surface thereof. Light is reflected from the surface of the disc closest to the flying head, as well as from the surface of the flying head assembly itself, and impinges onto a light sensor.
The flying height between the head and the disc can be determined by the intensity of the light received by the light sensor, or by the constructive or destructive wavelength of the light received by the light sensor. A computer is programmed to receive data from the flying height tester and calculates the perceived flying height and angle of the head. With the rapid advance of disc drive technology, the flying height of many modern disc drives is less than 0.1 microns. Therefore, the accuracy of the flying height tester, and therefore its calibration, is an important concern.
Calibration of flying height testers has been accomplished through the use of a standard head assembly whose characteristics are known. However, after repeated use, the reflective surface and flying characteristics of the standard head assembly can be altered by dust and other foreign matter, altering the calibration of the flying height tester. Calibration of flying height testers can also be accomplished through the use of a variety of calibration standards which are placed in the flying height tester.
One such standard used to calibrate a flying height tester comprises a substrate having a reflective layer deposited thereon to represent the head assembly and a transparent layer having a predetermined thickness deposited on the reflective layer. A disadvantage of such a calibration standard is that it uses a transparent material rather than air between the disc and the reflective layer.